1. Field of the Invention
The present invention relates to a lightning arrester installed at an uppermost part of a building to be protected, and more particularly to a lightning arrester capable of safely discharging charge, which is charged in an atmosphere adjacent to a building as thundercloud approaches the building, to the earth.
2. Description of the Prior Art
As generally known in the art, a lightning arrester is installed at an uppermost part of a building to be protected in order to safely discharge charge charged in a thundercloud to the earth by forming a discharge path between the thundercloud and the earth. In a fine day, an electric field in the earth is about 100V/m. However, if the thundercloud approaches, the electric field in the earth is about 10000V/m, and a potential difference between the earth and the thundercloud is about 100 million volts.
At this time, air existing in an atmospheric layer may act as a dielectric insulator in order to prevent a lightning stroke from being created between the earth and the thundercloud. Nevertheless, sometimes the lightning stroke can be created between the earth and the thundercloud.
Generally, a lightning arrester is installed at an uppermost part of a building to be protected in order to safely guide the lightning stroke into the earth. A Franklin rod type lightning arrester utilizes an electric field phenomenon called “tip effect”, in which an electric field is concentrated in a tip part of the lightning arrester.
A principle of the Franklin rod type lightning arrester is disclosed in various documents including Japanese Patent Laid-open Publication No. 62-216197 issued on Sep. 22, 1987.
The Franklin rod type lightning arrester utilizes spontaneously created natural phenomena so that it is operated only when a dielectric breakdown of air is created. Therefore, the Franklin rod type lightning arrester cannot effectively deal with the lightning stroke caused by a thundercloud, which does not make the dielectric breakdown of air. In order to effectively protect objects to be protected from the lightning stroke, various lightning arresters capable of effectively guiding charge charged in the thundercloud into the earth by discharging charge into an atmosphere as the thundercloud approaches the objects have been developed.
For example, French Patent Laid-open Publication No. 0096655 (issued on May 26, 1983) discloses a lightning arrester includes a main electrode grounded to an earth so as to allow ground charge to be concentrated on the main electrode through a tip effect, and an auxiliary electrode installed at a side of the main electrode in order to generate a stepped leader together with the main electrode by collecting charge distributed in an atmosphere. Discharge is generated between the main electrode and the auxiliary electrode. Ion charge is discharged into the atmosphere through the discharge process between the main electrode and the auxiliary electrode, so that a discharge path is easily formed between the thundercloud and the main electrode, thereby allowing charge in the thundercloud to be absorbed in the ground.
In addition, a lightning arrester disclosed in above Japanese Patent Laid-open Publication No. 62-216197 includes a collecting electrode for collecting charge, which is created when the thundercloud approaches the earth, from a peripheral area of the earth in order to induce discharge between an auxiliary electrode and a main electrode, and a high-voltage generating circuit having a determining section for determining a variation of charge generated from the collecting electrode. Charge of the collecting electrode is used as a power source of the high voltage generating circuit by recharging charge of the collecting electrode through a condenser. The high-voltage generating circuit is operated when the variation of charge exceeds a predetermined level, so that charge charged in the condenser is fed to a reactor, thereby generating discharge between the main electrode and the auxiliary electrode.
However, the lightning an ester disclosed in the above French Patent Laid-open Publication is installed at an uppermost part of a building to be protected so that an earth electric field induced by the thundercloud is inefficiently formed at the uppermost part of the building. Thus, if discharge is induced through filling charge contained in air, filling efficiency of charge is lowered so that discharge is difficult. For this reason, a discharge probability is lowered.
In addition, the lightning arrester disclosed in the above Japanese Patent Laid-open Publication uses a plurality of electronic components so not only is a structure of the lightning arrester complicated, but also it frequently requires exchange and repair works for the components of the lightning arrester installed at the uppermost part of the building.